The present invention relates to biodegradable polymer mixtures comprising    i) 40% to 95% by weight, based on the total weight of components i to ii, of at least one polyester based on aliphatic or aliphatic and aromatic dicarboxylic acids and aliphatic dihydroxy compounds;    ii) 5% to 60% by weight, based on the total weight of said components i to ii, of polyalkylene carbonate, particularly polypropylene carbonate;    iii) 0% to 60% by weight, based on the total weight of said components i to iii, of at least one biodegradable homo- or copolyester selected from the group consisting of polylactic acid, polycaprolactone and polyhydroxyalkanoate, and/or of an inorganic or organic filler;    iv) 0% to 10% by weight, based on the total weight of said components i to ii, of an epoxy-containing copolymer based on styrene, acrylic ester and/or methacrylic ester, and    v) 0% to 15% by weight of an additive selected from the group consisting of lubricant, antiblocking agent, antistat, UV absorber, UV stabilizer, thermal stabilizer, dye, pigment, colorant, plasticizer, fertilizer and active crop protection ingredient.
The present invention further relates to processes for producing biodegradable polymer mixtures, to the use of biodegradable polymer mixtures in the production of moldings, films or fibers and also moldings, films or fibers comprising biodegradable polymer mixtures.
Biodegradable mixtures comprising i) 20% to 5% by weight of a polyester based on aliphatic and aromatic dicarboxylic acids and aliphatic dihydroxy compound, ii) 20% to 80% by weight of polypropylene carbonate and iii) 60% to 15% by weight of polylactide are already known from WO 2007/125039. In these polymer mixtures, it is always the polypropylene carbonate, or the mixture of polypropylene carbonate and polylactic acid, which forms the continuous phase. Films comprising these mixtures are not always satisfactory with regard to their mechanical properties.
In practice, it is often difficult to achieve the desired combination of properties via mixtures. The properties of mixtures do not result additively from the properties of the individual components. Moreover, properties such as toughness and stiffness often trend in opposite directions. Furthermore, with some polymer mixtures, properties of individual components such as transparency and barrier effect are at least partly lost.